On 7/5/2015 12:10 PM, rickman wrote:
On 7/5/2015 10:48 AM, Ralph Mowery wrote:
"Ian Jackson" wrote in message
...
class-C PAs supposed to be around 66.%?). Also, as much power would be
dissipated in the PA stage as in the load.

I think this is easy to disprove in practice. I have an amp that is
probably class B, but it does not mater about the class. If I adjust
it to
an input of 2000 watts from the DC power supply, I get out 1200 watts
to a
resistive dummy load. If the above is true, I should have to input 2400
watts to the final stage. Now can someone tell me where the extra 400
watts
are comming from ? This 400 extra watts is not even counting on any
loss in
the circuits.

The idea of matched impedance transferring maximum power is one of those
"simplified" descriptions that has preconditions that some people forget
about. It is not a universal truth.

If you have a transmitter output with a fixed impedance you can get
maximum power transferred to the feed line by matching the feed line
impedance to the transmitter output impedance. But if your feed line
impedance is the constant, you get maximum power transfer by minimizing
the transmitter output impedance, meaning zero ohms.

So you could in theory get 1200 watts into your feed line while drawing
only 1200 watts from the power supply.


So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick? Hint: Sophomore-level AC Circuits course in virtually
any EE degree, and anyone claiming an EE degree should be able to tell why.

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On Sun, 05 Jul 2015 16:32:49 -0400, Jerry Stuckle
wrote:

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick? Hint: Sophomore-level AC Circuits course in virtually
any EE degree, and anyone claiming an EE degree should be able to tell why.

Actually, there are low output impedance RF power amps. They're quite
common in NMR power amps to reduce coupling between stages:

Ultra-low output impedance RF power amplifier for parallel excitation
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663597/

Ultra-low Output Impedance RF Power Amplifier Array
http://cds.ismrm.org/ismrm-2007/files/00172.pdf


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 7/5/2015 6:48 PM, Jeff Liebermann wrote:
On Sun, 05 Jul 2015 16:32:49 -0400, Jerry Stuckle
wrote:

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick? Hint: Sophomore-level AC Circuits course in virtually
any EE degree, and anyone claiming an EE degree should be able to tell why.

Actually, there are low output impedance RF power amps. They're quite
common in NMR power amps to reduce coupling between stages:

Ultra-low output impedance RF power amplifier for parallel excitation
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663597/

Ultra-low Output Impedance RF Power Amplifier Array
http://cds.ismrm.org/ismrm-2007/files/00172.pdf



We're not talking amateur transmitters, troll. Try to stay on topic -
if that's at all possible.

--
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Jerry Stuckle

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On Sun, 05 Jul 2015 20:05:17 -0400, Jerry Stuckle
wrote:

On 7/5/2015 6:48 PM, Jeff Liebermann wrote:
On Sun, 05 Jul 2015 16:32:49 -0400, Jerry Stuckle
wrote:

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick? Hint: Sophomore-level AC Circuits course in virtually
any EE degree, and anyone claiming an EE degree should be able to tell why.

Actually, there are low output impedance RF power amps. They're quite
common in NMR power amps to reduce coupling between stages:

Ultra-low output impedance RF power amplifier for parallel excitation
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663597/

Ultra-low Output Impedance RF Power Amplifier Array
http://cds.ismrm.org/ismrm-2007/files/00172.pdf

We're not talking amateur transmitters, troll. Try to stay on topic -
if that's at all possible.

NMR is Nuclear Magnetic Resonance. To the best of my knowledge,
medical imaging in not performed by amateurs. I realize that the
translation from Chinese to English is somewhat lacking in the above
articles. I think if you make the effort, you might learn something
about low output impedance power amplifiers, which seems to be a topic
drift that *YOU* started with the above "1 ohm" question. Since the
original question of the purpose of the matching transformer on the 43
ft vertical has been correctly answered at least 3 times, I would
guess that some topic drift might be acceptable. Do continue.

Since the original question is addressed to Rick, I won't ruin your
fun by providing an answer. No need to thank me.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 7/5/2015 8:23 PM, Jeff Liebermann wrote:
On Sun, 05 Jul 2015 20:05:17 -0400, Jerry Stuckle
wrote:

On 7/5/2015 6:48 PM, Jeff Liebermann wrote:
On Sun, 05 Jul 2015 16:32:49 -0400, Jerry Stuckle
wrote:

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick? Hint: Sophomore-level AC Circuits course in virtually
any EE degree, and anyone claiming an EE degree should be able to tell why.

Actually, there are low output impedance RF power amps. They're quite
common in NMR power amps to reduce coupling between stages:

Ultra-low output impedance RF power amplifier for parallel excitation
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663597/

Ultra-low Output Impedance RF Power Amplifier Array
http://cds.ismrm.org/ismrm-2007/files/00172.pdf

We're not talking amateur transmitters, troll. Try to stay on topic -
if that's at all possible.

NMR is Nuclear Magnetic Resonance. To the best of my knowledge,
medical imaging in not performed by amateurs. I realize that the
translation from Chinese to English is somewhat lacking in the above
articles. I think if you make the effort, you might learn something
about low output impedance power amplifiers, which seems to be a topic
drift that *YOU* started with the above "1 ohm" question. Since the
original question of the purpose of the matching transformer on the 43
ft vertical has been correctly answered at least 3 times, I would
guess that some topic drift might be acceptable. Do continue.

Since the original question is addressed to Rick, I won't ruin your
fun by providing an answer. No need to thank me.


We're not talking about NMR. We're discussing amateur ratio.

Try to stay on target, troll.

And no, I didn't start ANY topic on output impedance drift. But you're
too stoopid to understand the topic at hand, so I can see how you can
come to that conclusion.

Fortunately, intelligent people understand the thread and the fact I
didn't start the topic on impedance drift. The fact you think I did
proves your stoopidity.

As well as the fact that amateurs have anything to do with NMR.

--
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Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote:
On 7/5/2015 6:48 PM, Jeff Liebermann wrote:
On Sun, 05 Jul 2015 16:32:49 -0400, Jerry Stuckle
wrote:

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick? Hint: Sophomore-level AC Circuits course in virtually
any EE degree, and anyone claiming an EE degree should be able to tell why.

Actually, there are low output impedance RF power amps. They're quite
common in NMR power amps to reduce coupling between stages:

Ultra-low output impedance RF power amplifier for parallel excitation
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663597/

Ultra-low Output Impedance RF Power Amplifier Array
http://cds.ismrm.org/ismrm-2007/files/00172.pdf



We're not talking amateur transmitters, troll. Try to stay on topic -
if that's at all possible.

What kind of transmitters should be talk about in an amateur group?

Are amateur transmitters different than any other kind of transmitter?


--
Jim Pennino

In message , Jerry Stuckle
writes

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick?

They probably would - if they could (at least for some applications).
That would then enable you to step up the TX output voltage (using a
transformer), so that you could drive more power into a higher (eg 50
ohm) load.

But of course, the overall output impedance would then become
correspondingly higher. You would also be drawing correspondingly more
current from the original 1 ohm source, and if you used too high a
step-up, you would risk exceeding the permitted internal power
dissipation (and other performance parameters).

So yes, you are getting more power output when you match* the source
impedance to the load - but it doesn't necessarily mean you always can
(or should) go the whole hog.
*Or, at least, partially match.



--
Ian

Ian Jackson wrote:

In message , Jerry Stuckle
writes

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick?

They probably would - if they could (at least for some applications).
That would then enable you to step up the TX output voltage (using a
transformer), so that you could drive more power into a higher (eg 50
ohm) load.

But of course, the overall output impedance would then become
correspondingly higher. You would also be drawing correspondingly more
current from the original 1 ohm source, and if you used too high a
step-up, you would risk exceeding the permitted internal power
dissipation (and other performance parameters).

So yes, you are getting more power output when you match* the source
impedance to the load - but it doesn't necessarily mean you always can
(or should) go the whole hog.
*Or, at least, partially match.

No, honestly, you're not getting more power output when you match the
load to the source. *If* you have a *given* voltage generator with a
*given* source impedance, then yes: that situation arises, for
instance, if you have a very low noise amplifier with given output
characteristics and you want to extract the maximum signal power in
order to maintain the best noise factor through stages of amplification.
But when you are designing a PA you start with a pile of components (or
a catalogue of same) and you choose your voltage swing and current
capacity to put as much power in the load as you want to (limited
largely by the heat dissipation of the output devices in a practical
circuit) and design the circuit to dissipate as little power in the
amplifier as you can. You are *not* interested in transferring as much
power as you can from a given circuit. It may only be tenth of the
power output that you could get (ignoring practical dissipation limits)
from a certain voltage with a different load, or a higher voltage with
the same load (which you could achieve with a transformer), but that is
irrelevant. Among other things, you are likely to end up with a low
source impedance compared with the load and that makes no difference to
the operation of the transmission line or aerial.



--
Roger Hayter

On 7/7/2015 6:17 AM, Ian Jackson wrote:
In message , Jerry Stuckle
writes

So why don't manufacturers design transmitters with 1 ohm output
impedance, Rick?

They probably would - if they could (at least for some applications).
That would then enable you to step up the TX output voltage (using a
transformer), so that you could drive more power into a higher (eg 50
ohm) load.


Oh, it's completely possible. It's just a matching network, anyway -
one which has to be in place anyway, because the output of a tube amp is
relatively high impedance, and the output of a transistor amp is
relatively low impedance. In fact, a 144W transistor amp running on 12V
wouldn't even need a matching network. It's output would have 1 ohm
impedance.

But of course, the overall output impedance would then become
correspondingly higher. You would also be drawing correspondingly more
current from the original 1 ohm source, and if you used too high a
step-up, you would risk exceeding the permitted internal power
dissipation (and other performance parameters).


And why would the output impedance change just because the load
impedance changes? They are two separate things.

But according to you, no step-up is required - you can drive any
(comparatively) high impedance source most efficiently from a low impedance.

So yes, you are getting more power output when you match* the source
impedance to the load - but it doesn't necessarily mean you always can
(or should) go the whole hog.
*Or, at least, partially match.


So, which is it? First you say the output impedance of the transmitter
should be very low for maximum power to the antenna. Now you say it
should be matched. Then you say it shouldn't be matched.

Which is it?

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